Multiple furnace fluid heating unit



March 30, 1954 w. H. ROWAND ETAL MULTIPLE FURNACE FLUID HEATING UNIT Filed March 1 1950 INVENTORS I/VIY/ ff lean/017a 5 BY Char/esSSim'i/z V. as-EM Y E N m w A Patented Mar. 30, 1954 2,673,553 MULTIPLE FURNACE FLUID HEATING UNIT Will H. Rowand, Madison, and Charles S. Smith,

tion of New Jersey assignors to Wilcox Company, New York,

The Babcock & N. Y., a corpora- Application March 1, 1950, Serial No. 147,102

8 Claims. 1

This invention relates to improvements in steam generators.

The invention more particularly relates to a type of steam generating installation including a superheater, a turbine, and a reheater.

It is an object of this invention to provide a steam generating installation in which the component parts, and particularly the superheater and reheater, are so constructed and arranged that the steam termined steam temperature at the outlet of the reheater.

The invention is exemplified by a steam generating and steam superheating installation in which highly superheated steam at high preshigh pressure turbine and then at the resultant exhaust pressure is returned to the installation for superheating by reheating to a high degree for further expansion through a relatively low pressure turbine exhausting to a condenser.

In installations of this character where the steam is generated at a high pressure (which may be of the order of 1500 p. s. i. to 2500 p. s. i.) both the initial superheating and the reheat superheating is most advantageous it carried out to correspondingly high temperatures of the order of 950 F. or above.

With regenerative heating of the feed water by bleeding steam from selected stages of the steam turbines, the withdrawal of steam for such heating from the high pressure turbine allows only a fraction of the initial steam flow to pass from the exhaust of the high pressure turbine to the steam reheater. In other words the reheater is normally called upon to reheat a smaller quantity of steam than that flowing through the initial or primary superheater.

a In orderto attain a high degree or reheat superheating it is desirable to subject the reheater to high temperature gases, yet due tothe fact that no steam flows through the reheater until the turbine is in operation, provision must be made to avoid overheating the reheater tubes by subjecting them to hot gases prior to steam flow therethrough.

The present invention provides an arrange;

ment of a pair of fuel burning furnaces so reeiel li fe e etaee s p e te surface-8 that:

the respective surfaces perheated high pressure steam and the reheated steam to the optimum high value for high thermal efficiency of the turbine.

Two furnaces, each with its complement of fuel burners, are provided. Both furnaces are defined by Water cooled walls and the heat absorption of the walls generates the major portion of the steam and reduces the temperature of the products of combustion to a degree related to the fusion temperature characteristics of the ash in the coal, where such fuel is used.

One furnace delivers products of combustion directly to the primary superheater for the high pressure steam. The other furnace delivers perheater.

generate high pressure steam, reheat low preshigh pressure steam and superheat high pressure steam.

When the furnace volumes and heat absorbing surfaces are so arranged that of the total heat of the fuel is introduced into the second furnace serving the reheater, while 30% is introduced into the furnace serving the primary superheater directly, regulation of the distribution of the relative fuel inputs to the two furnaces as the rate of steam a furnace which of steam generating tubes into two component furnaces. The latter are separately fired, one being fired from the standpoint of the requirements of reheat control, with the gases flowing through a convection pass across the tubular elements of a steam reheater. Beyond the reheater these gases join the gases from the other part of the furnace. The combined gases then pass through another convection pass in which there is located a convection superheater. The'latter may be divided into two sections with the steam flowing from the steam and water drum through the first section of the superheater, and then to an attemperator which is operated to control the final superheat temperature. From the attemperator", the steam flows to the second section of the superheater, and from that section of the superheater to a turbine. From a lower stage of the turbine, steam flows through the tubular elements of the reheater. 4 I

The novel features of our invention are pointed out with particularity in the appended claims, but in order that the invention may be clearly understood, it will now be described in detail, in

connection with the accompanying drawing showing anillustrative embodiment of the invention.

In saiddrawing the figure is a diagrammatic view in the nature of a sectional elevation.

The drawing discloses a large volume furnace l defined by wall tubes some of which connect the lower headers l2 and- M to the steam and water drum l5, as illustrated. Similar wall tubes and headers are provided for the remaining furnace walls. The gases pass from the upper part of this furnace to a gas outlet in which are disposed the sections 18-2 l, inclusive, of a convection superheater.

Steam passes from the steam and water drum through connectors such as 24 and 26 to the superheater inlet header 28-. From that header the steam flows through the upright tubes of the superheater section 18, and then successively through the tubesof the superheater section l9 to the intermediate superheater header 30. From that header the steam flows through a conduit 32 to an attemperator 34. From the attemperator. steam flows through the conduit 36 to a second intermediate header 38, and thence through sue-1 cessivesuperheater tubes of the superheater sections 2| and 22 to the superheater outlet header 40.

Adjoining the furnace I0 is a similar furnace 42, the gases from which are discharged into the upper part of the furnace l0 across the tubular screen formed by the upper sections of tubes 44 and 46. The lower sections of these tubes delineate a furnace separating wall 48 common. to both furnaces l0 and 42. Some of the tubes forming the wall 48 are connected at their lower ends to the submerged header 50- and other wall tubes of the furnace 42 along wall 52 connect the submerged header 54 with the steam and water drum IS. The remaining walls of furnace 42 include similar wall tubes and appropriate lower headers, the latter, with the headers 12 and H being connected to the drum l6 by suitable down comers.

The gases from the furnace 42 pass across successive series connected tubes of the reheater'sections 56 and 58 and then enter the upper part of the furnace [0 adjacent the superheater.

The furnace I0 is fired by pulverized coal bumers such as those illustrated at 60 and B2, and the. furnace 42 is fired by similar burners as indicated at 64 and 66.

In. the operation of the illustrative installation, the reheater including the. section'sw-and 4 58 is heated only by the gases from the furnace 42, and, consequently, danger of overheating the tubes of the reheater is minimized by so controlling the operation of the furnace 42 that it does not discharge gases across the reheater until steam is passing through the latter.

The reheater receives-steam from an intermediate stage of a turbine operated by steam supplied by the steam generator. This steam supply to the reheater is at a pressure lower than the pressure of the steam supplied to the superheater, and with this arrangement there is no steam flow through the reheater until after the turbine is in operation.

When 4 0% of the total heat input to the installation is being supplied by the furnace 42 and the remaining 30% of the total input supplied by the furnace Hi, the illustrative installation will maintain control of superheat and reheat from down to about 65% of total capacity. From capacity down to 90% superheat is controlled by the attemperator indicated at 34 in the drawing.

The invention is particularly applicable to installations operating at superheat and reheat temperatures of the order of 1000 F.. where the heat required for superheating and. reheating is a high percentage of the total heat.

Each of the steam heaters, the superheater and the reheater, is of the vertical tube type. Furthermore, there is no tubular screen immediately in front of each of the steam heaters.

The furnace gases pass from chamber A, above the combustion chamber 42 across the tubes of the reheater sections 56 to 58 and then across the screen tubes 44 and 46 into the chamber B which acts as a mixing chamber for the gases from the different furnaces to provide a uniform temperature of the gases crossing the superheater sections 18-2 l inclusive.

The chamber A is disposed at the top of combustion chamber 42 and has a lateral outlet from which the gases pass to the chamber B and the latter has a side inlet for furnace gases from the combustion chamber l0.

The superheater sections 20 and 21- are protected from radiant heat directly transmitted from thecombustion chamber I0 by the arch 10 having the downwardly inclined upper wall 12 and the upwardly inclined lower wall 14. These wallsconverge at C and are delineated by portions of the wall tubes 16 along the wall 18 of the combustion chamber II). This arch 10 also acts to prevent cooler gases from the furnace 42' from coming down into the furnace Ill.

The screen comprising the tubes 44 and 46' acts to protect the reheater from high temperature furnace gases in the furnace l0 and the tubes 48 have intermediate portions such as 80 and 82 bent to form the. arch- 84 which extends from the commonwall 48 to a position above the midportion of the furnace 42. Thus, by virtue of the arch construction 84 and the screen comprising the tubes 44 and 46, there is very little heat transfer from the furnace i 0 to the reheater when only the furnace I0 is in operation.

When the illustrative installation is operating at pressures in excess of 1500 p. s. i. and at superheats of the order of 1000 F., the installation is controlled by'varying theop'eration of the burners of the furnaces I 0 and 42 to maintain control of steam superheating and reheating over a wide load range.

Although-the invention is desoribcfwith refer? upper parts of the respective furnaces; said boundary vapor generating wall tubes generating at least the predominant proportion of the total vapor generated by the unit; a reheater; a superheater; some of said tubes also presenting a wall common to the furnaces with some of the tubes of this common wall also formcharging those gases toward the superheater gas pass and at such a position adjacent thereto as to by-pass the main part of the superheater furnace; fuel burning means disposed inthe furnace Walls and directing combustion elements along and interposed relative to the superheater, on the one hand, and the firing means for the superheater furnace, on the other hand; said fuel burning means normally furnaces independently of each other with the reheater furnace being fired from the standpoint of the requirements of reheat control.

2. In a high pressure steam generating unit, steam generating wall tubes delineating a first combustion chamber or furnace of large volume and constituting the major part of the total steam generating surface of said unit, means for firing the furnace, some of said steam generating tubes being bent into arch forming arrangement to delineate an arch extending over a major part of said combustion chamber, refractory material closing the spaces between the arch delineating tubes and completing the arch, a convection superheater including a bank of series connected upright tubes disposed above said arch and across the path of gas flow in a gas pass leading from said combustion chamber, the. disposition of the superheater tubes over the arch being such that the arch affords a radiant heat screen interposed relative to the superheater and the predominating proportion of the combustion chamber, other steam generating tubes delineating a second large volume furnace or combustion chamber having its gas outlet in the upper part of a wall common to both combustion chambers, some of said other tubes delineating said common wall having intermediate parts extending in arch forming arrangement at the upper part of the second combustion chambers, means for separately firing said second combustion chamber, a convection reheater including a bank of series connected upright return bend tubes disposed directly above said last mentioned arch forming tubes and disposed across the path of gas flow in a reheater gas pass leading from the second combustion chamber, and means including a steam and water drum having the upper ends of the steam generating tubes connected thereto and supplying steam for the superheater, the reheater being subject to a minimum of heat absorption while the entire superheater is heated to an operative degree.

3. In a superheater and reheater steam generating unit, first and second furnaces having their boundary surfaces defined by steam generating wall tubes generating substantially all the steam provided by the unit, means forming a single gas outlet passage through which the furnace gases from both furnaces must flow, the entrance to said passage covering only a minor side of the first furnace, convection zone offset relative to the major parts of the furnaces, a radiant heat protector baffle means disposed laterally of and extending longitudinally of said zone and interposed relative to the main parts of the furnaces and the steam heating means, a part of the steam heating means constituting a superheater always subject to combined gas flow from the multiple furnaces, a second part of the steam heating means constituting a reheater subject to gas flow from the second of 4. In a reheater and superheater steam generating unit, steam generating wall tubes defining a plurality of vertically elongated large volume furnace chambers having a common wall formed by some of the wall tubes, one of said furnace chambers being a reheater furnace chamber and the other a superheater furnace chamber, said steam generating wall tubes generating substan tially all of the steam produced by the unit, a reheater gas pass leading laterally from the upper part of one furnace chamber to the upper part of the other, a convection reheater in said gas pass and disposed at an elevation above the major part of reheater furnace hamber, a superheater gas pass disposed wholly at an elevation above that of the main part of the superheater furnace chamber and leading laterally therefrom at a position adjacent the gas outlet of the reheater gas pass, a convection superheater in the superheater gas pass subject to a predominant proportion of the total flow of the gases from both furnaces, means conducting steam from the wall tubes to the superheater, and means separately firing said furnace chambers.

5. In a superheater and reheater multiple furnace steam generating unit, multiple furnaces having their boundary surface defined by steam generating wall tubes generating the preponderance of the steam provided by the entire unit, some of said steam generating tubes being disposed so as to define a wall common to first and second furnaces, wall means defining a superheater gas pass and a reheater gas pass, said Wall means including a nose battle for each furnace, a convection superheater with its elements disposed transversely of gas fiow through the superheater gas pass leading from outlet of the first furnace, a convection steam reheater with its tubular components disposed transversely of gas fiow through the reheater gas pass leading from the gas outlet of the second furnace, said furnaces having their gas outlets disposed in similar offset relation to the main parts of the furnaces so as to co-act with said gas passes to present unidirectional gas flow through both furnace outlets and over both reheater and superheater, the reheater and the gas outlet of the 7 second: furnace being disposed so as to race citrectly toward the gas outlet of the first furnace, and means for indep'enrlently firing saidfur-- naces.

6-. A fluid heating unit comprising means in cluding vapor. generating" wall tubes defining a first vertically elongated furnace chamber and a gas pass extending laterally from the upper' part of said furnace chamber; vapor superheat-ing tubes positioned in said gas" pass; means including other vapor generating wall tubes defining a second vertically elongated furnace chamberhaving a commonwall with said first furnace" chamber, means forming a second gas pass extending laterally from the upper part of said second furnace chamber and arranged to discharge heating gases from said second furnace chamber toward and over said vapor'superheat ing tubes, vapor reheating tubespositionedin said second gas pass; means for' independently firing said furnace chambers, the firing means directed from opposite furnace chamber walls toward said common wall, the majoripart' of the total steam from the unit being generated in said wall tubes prior; to the contact of the furnace gases with the vapor superheatlng tube surfaces, and means conducting the wall tube generated vapor to the vapor superhe'ating tubes.

7. A steam generating, steam superheating,

and steam reheating, unit in which substantially all ofthe steam is generated in wall tubes defining the roofs and walls of separate vertically elongated furnaces, afirst steam heater convectionally heated'only by the gases from one of said furnace chambers. a second steam heater convectionally heated by the gases from both furnaces,.separately controllable sets of fuel burnersoassociatedwith the. respective furnaces and positioned in the lower portions of the furnaces.

a predominantly radiantly heated wall common to both furnaces,.said Wall including. a row of. closely spacedsteam. generating wall tubes ex.- posed on opposite sidesto the directradiant heat of the furnacemmeansforming heating gas flow passagesleading laterally fromcnly the upper portions of saidrfurnaces bothof said gas flow passages being limitedto positions adjacent the unit, the gas passages and upper part of the their inletsbeing; so. constructed and arranged relative to the fuel vburners'that the gas flow in the furnaces is mainly upward to'the gasinlets and the gas flow through said passages is mainly transverse to the gas flow in the furnaces, means presenting convection steam heating surfaces so arranged with respect to'each of'saidgas outlets merits towards opposite that-heating gases-now train atle'ast sneer salufurnaces pass thereo'ver, the" convection steam heater' surface directly nace being predominantly for high pressure steam superheating while the convection steam heating surface associated with the other furname is predominantly for low pressure steam passage associated with reheating, the gas flow one" of the furnace outlets constituting a con necting passage between the furnaces.

8s In a vapor generating unit, a vapor and liquid drum" adjacent the upper part of the unit, liquid headers adjacent the lower part of the unit, vapor generating wait tubes extending from the drum t'o'said headers" and defining the roof and other boundaries of" reheater and superheater furnaces and also defining the boundaries ofreheater and superheater'gas passes leading laterally from the upperpa'rts of the respective furnaces, a reheater, a super-heater, some of said tubes also presenting a wall common' tothe furnaces with parts of some of 'the tubes of this common wall also defining a radiant heat shield interposed relative to the reheater' and-the-major part of the'reheater furnace, the reheater gas pass re'ceivingallof the gas generated by the reheat'er furnace, fuel burning means disposed in the furnace walls opposite said common wall and directing" combustion elesidesof said common wall, and a radiant heat shield int'erpos'ed relative' to the superheater and'the' firing means for the superheater furnace, said firing means nor-'- mally operating to fire thefurn'a'c'e's independently of' each other with the reheater' furnace being fired from thestandpo'int' of' the requirements of reheat control.

WILL H". ROWAND.

CHARLES S. SMITH.

associated with onefur-- 

